I am researching possible amplifier kits to be used with an Orion type loudspeaker. As with the Orion, I would require either 6 channels with the woofers getting 100 watts or 8 channels of 60 watts or so.

I've checked out the AKSA 55 (and 100) and the ESP P3A. Both seem like good options and are within my projected budget (under 1500 US$). Has anyone had a chance to compare the two for quality of sound? Also, are there any other designs I should consider? I wish to have as good sonics as possible, though I've pretty much ruled out Class A amps due to the excessive heat (with a certain amount of regret).

Originally posted by millwood have you checked out those commercial products? ATI for example charges $200 per channel (180wrms into 8ohm), fully assembled and tested...

Yes, I have checked them out and am still doing so.

I agree that there doesn't appear to be a big price differential. According to the $200 price for an ATI module, an ATI '1806' would cost $1800 and would be suitable, if not ideal. Mr. Linkwitz recommends the ATI 6012 since it provides 12 channels allowing one for each woofer which drives them better. But the 6012 costs $2k.

Part of the problem is the fact that I need either 6 or 8 channels, instead of 5 or 7 as the commercial products are typically configured. Going commercial basically limits me to 6 channels (except for the 6012). I then either have too much power for the mids and tweets or too little for the woofers. Otherwise, I'd just buy used. I may do that anyway if I find a good deal. I suppose I could limit the output to the mids and tweets using the Behringer DCX-2496 I plan to use.

I'm really stretching to save money here. My thought is to build the amps into the bottom of the woofer cabinets. That way, I may save on casework, cables and connectors. My current pricing has the P3A route costing me less than $1200 and the ASKA route between $1100 and $1400.

The AKSA is very well reviewed and is in kit form.
Altough I never built one I think it can be a excellent choice.

The P3A is also very good sounding, I've built a pair myself with off-the shelf components and it was comparable (altough less powerful) with the Holton's Symamp.
With an accurate component selection I tink it can take off, but if you aren't willing to experiment and to search go for the AKSA, Hugh Dean will thank you and provide a complete kit.
Also Rod Elliot is very helpful, if you decide to go for the P3A, but AFAIK he only sells the PCBs (at a attractive price!), so the component choice is up to you.

I have both the AKSA 55 and Elliott P3A amps. Both are good amps. I built them using exactly the same power supply and output transistors so I could get a direct comparison. I was interested in their different design philosophies, ie EF vs CF output stages, different constant current feed cct, and generic components vs higher quality components.

The AKSA is well burnt-in as it is over 18 months old now and the P3A would have had a few weeks burn-in. The AKSA is built with components supplied by Hugh and the P3A is build from generic components (other than the output transistors).

While I find it difficult to put in words the difference between the two amps, suffice to say, the last time I plugged the AKSA in, I promptly logged onto the net and bought another one with the Nirvana upgrade.

The 55W amp sounds sweet, clear and musical but has insufficient grunt for medium or low efficiency speakers with extended bass response. It works very well as the treble amp in an active system.

I marginally prefer the sound of the P3A to the AKSA 100N. Both are capable of very good sound quality, the AKSA is slightly warmer and more colourful (coloured?) the P3A is clearer and more controlled at the frequency extremes. OTOH, I believe I saw a post by Nelson Pass stating he marginally preferred the AKSA and he has collosal amounts more audio cred than me!

To put this into perspective the AKSA and P3A are vastly superior to a Linn LK140 (UKŁ750) I used to own, they also outperformed a Lindsley Hood 80W Mosfet amp and various Borbely imposters I have built.

Please also note that unlike Greg's my P3A has (what I would consider to be) a better power supply than the AKSA 100N.

The AKSA uses 9,400uF per rail per module on the 100W Nirvana, and ultrafast soft recovery diodes. Considering the P3A uses the same capacitance, and a run-of-the-mill, 35A rectifier bridge, but a back-to-back diode/10R resistor/100nF cap all in series between signal and power earth.

I am guessing, but would like confirmation, that it is the diode/R/C link between power and signal earth which you believe makes the P3A supply 'superior'.

Have you tried the UFSR diodes against a conventional 35A bridge? I believe you would be surprised, though I suspect you have already,

I'd be interested in a bit more details on your power supplies for the P3A. I'm always interested in trying a few new things. I'm guessing you didn't build the standard P3A power supply.

How do the Sanken output devices compare to the Toshiba ones?

On a side note: One thing I don't understand is, I've found my AKSA 55 more than powerful enough to drive my inefficient 84db speakers. Even my LM1875 gainclones (< 20 watts?) are capable of driving my speakers to a level loud enough for day to day listening. Is 84db considered to be medium or low efficiency? Are my speakers incorrectly rated? Or does the fact that the crossover is only used on the tweeters make the difference?

The P3A is built on the standard pcb with some track modifications to allow dual mono construction. I used different power semiconductors – the VAS transistor (BD140) was replaced by 2SA1360, the drivers (BD139, BD140) were replaced by 2SA1306/2SC3298 and the output devices are 2SC2922/2SA1216. The Sanken output transistors were used to enable 4 Ohm loads to be driven with 42V rails without resorting to paralleled devices. The power supply for each channel consists of a 225VA 30-0-30VAC toroid with MUR820 diodes (one bridge per rail) and BHC ALS20A 10,000uF 63V capacitors (one per rail). I found it necessary to add a 10uF capacitor across the Vbe multiplier to provide sufficient drive to the negative side of the output stage when driving low impedance or capacitive loads. Using a bench power supply with 1ft long leads the on-board decoupling capacitors (0.1uF) were found to be inadequate, resulting in oscillation into capacitive loads. I replaced these with 56uF 63V Panasonic HFQ capacitors (in the chassis this may not be necessary due to the close proximity of the main reservoir capacitors, however I left them in place). I also added an output inductor and resistor to ensure stability into highly reactive loads, without this the amplifier could be provoked into oscillation. No input coupling capacitor is fitted since my preamp’s output is capacitively coupled.

Greg - my comment about the power versus efficiency is not related to loudness, rather to subjective scale, power and depth in the bass. The AKSA 55 just is not as convincing here as the AKSA 100, even at medium volume levels. I have not compared the Sankens to the Toshs directly (in an identical amp), so I don't feel able to state the differences athough I can conclude it's possible to get both to sound excellent. BTW how does the AKSA compare to the gainclone? - I gave up with chip amps after getting average results from TDA1541s.

Hugh - I did not use an RC snubber across the mains switch in the P3A nor are there any 10R ground lift resistors. I hope I got the grounding well sorted and therefore don't need the 10R resistors - there is certainly zero measurable or audible hum at quiescent.